The present invention relates to a vehicle suspension device for supporting rear wheels on a vehicle body.
A suspension system has been known in which a suspension cross member on which a suspension member for rear wheels and a differential (differential gear) are mounted is mounted on a vehicle body via elastic mounts (cylindrical mounts) provided at two positions at two front and rear positions of its lateral ends, and vibration and noise transmitted from the rear wheels or the differential while a vehicle is running is cut off to improve the vehicle""s comfort to ride, for example, as disclosed in Japanese Unexamined Patent Publication No. HEI 7-315245.
In the case that the front and rear ends of the suspension cross member on which the suspension member is mounted are mounted on the vehicle body via the elastic mounts (as elastic mounting means) including rubber bushes as described above, no sufficient bearing strength of the suspension cross member can be ensured. Accordingly, when the vehicle is making a turn or the like, the elastic mounts are deformed by a lateral force transmitted from the rear wheels, thereby changing an alignment of the rear wheels to disadvantageously reduce running stability.
Further, in a vehicle in which a rigid frame (power plant frame) is provided to couple a power unit at the front part of a vehicle body and a differential at the rear part of the vehicle body in order to suppress a wind-up of the differential in response to a torque reaction force transmitted from rear wheels, which are drive wheels, while the vehicle is running, a suspension cross member on which the differential is mounted may be supported on the vehicle body by elastic mounts as disclosed in Japanese Unexamined Patent Publication No. HEI 4-238781. In such a case, vibration transmitted to the suspension cross member from the rear wheels is transmitted to the power unit via the differential and the rigid frame, thereby presenting a problem that additional vibration of the power unit is unavoidable.
In order to suppress transmission of the vibration of the power unit to the vehicle body and improve the running stability of the vehicle by suppressing a change in the wheel alignment, a large value has been set as a spring constant of the mounts for mounting the front and rear ends of the suspension cross member for the rear wheels on the vehicle body or the suspension cross member has been firmly mounted on the vehicle body via rigid mounts including metallic bushes. However, in such a case, vibration and noise transmitted from the rear wheels and the like to the vehicle body while the vehicle is running cannot be effectively reduced, presenting a problem of unavoidably making the vehicle uncomfortable to ride.
In view of the problems residing in the prior art, an object of the present invention is to provide an vehicle suspension device capable of effectively suppressing a change in wheel alignment when a vehicle is making a turn and the like without reducing the vehicle""s comfort to ride.
The present invention is directed to a suspension system for a vehicle, comprising a suspension cross member; a suspension member for a rear wheel supported on the suspension cross member; first type elastic mounting means for mounting the suspension cross member on a vehicle body, the first type elastic mounting means being mounted at three positions along forward and backward directions of the vehicle body and forming a triangle when the vehicle body is viewed sideways; a rigid frame for coupling a power unit provided at a front part of the vehicle body to a differential provided at a rear part of the vehicle body; and second type elastic mounting means for mounting the differential on the suspension cross member, a spring constant of the second elastic mounts being set smaller than that of the first type elastic mounting means.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.